Film claw



0. WITTEL April 6, 1937.

FILM CLAW Filed Nov. 29, 1935 .PRIOR ART 'I'bis application is a continuation-impart of T Patented Apr. 6,

FILM CLAW Otto Wittel, Rochester, N. Y., assignor, by inesne ts, to Eastman Kodak Company, Jersey City, N. 1., a corporation of New Jersey Application November as, 1935, Serial No. 52,005

Claims. (01. 88-18.!)

spring tension in the film gate is tightened to patent application SerialNo. 758,947, filed December 24, 1934, which was entitled Film claw," and of which Otto Wittel is the inventor.

This invention relates to photography and more particularly to the film claw in a ratchet type pull-down mechanism for intermittently moving a cinematographic film strip.

Tothoseskilledintheartitis awellknown fact that with intermittent pulldown mechanisms of the ratchet type a certain amount of difiiciilty arises in maintaining the film claw in the film perforations throughout the length of each film advancing stroke of said claw, and in order to get satisfactory results in mechanisms using thisform of film advancing means it isabsolutely essential that the claw be maintained in the film perforations until the advancing stroke is completed. Up to the present time much 90 difiiculty has been encountered in film advancing means of the ratchet type due to the tendency of the claw to hop out of the film perforations before the advancing stroke is completed.

In a movement of this kind when the claw slips 25 out of the engaged perforation before the end of the film advancing stroke it subsequently s causes a misframing of the next picture with relationto the lens system, and at the same time the lower take-up loop in the film path is short- 30 ened by an amount equal to the length of the film advancing stroke not completed. It is obvious therefore, thata few repetitions of these incompleted strokes finally cause the loss of the 7 lower take-up loop in the film path thereby ne- 35 cessitating a shut-down, because the take-up means then pulls the film through the film gate in a continuous manner. a g Of the several different means previously used to insure the engagement of the claw -and the film perforations, probably the spring pressing means which constantly acts against the claw to press it against the film, and the use of a claw having a sharply inclined film engaging i'ace wherein the nose of the claw during engagement 45 with the film perforations is below the engaged edge of theperforatlon, are most common.

The spring pressing methodmentioned above works satisfactorily as long as the exact tension required can be incorporated in the spring. but

1: the tension becomes'too loose the spring is useless, while if the tensionis too great it tends to cause an unsteadiness in the film movement due to the fact that the claw tends to reverse the film strip momentarily on its upstroke in- 55 stead of leaving the perforation cleanly. If the overcome this latter dlfilculty then the pull on the-film by the take-up means is usually increased to a point where the driving motor is presents severaldifiiculties. In the first place,-

in order to insure steadiness in the picture frame of the film strip it is absolutely essential that the film claw advance thafilm strip an equal amount during each advancing stroke thereof, and this requirement necessitates the claw leaving the successive film perforations at identical points relative to the lens system. In a pull-down mechanism of the ratchet type it is almost impossible to control the distance to which the claw penetrates the film perforations and insure that on each stroke of the claw the depth of penetration is exactly the'same, particularly at the end of the advancing stroke. Therefore, if a claw having a sharply inclined film engaging face is used, any variation in the depth of penetration of said claw into the film perforations between the successive advanci'ng strokes thereof will cause a variation in the length of film' advanced at each stroke because the claw will failto leave each successive engaged perforation at the same point relative to the lens system.

Although this variation may seem negligible, an unsteadiness in the picture frame will occur.

regardless of any variationin the penetration of said claw into the engaged film perforation,

a straight or substantially horizontal film engaging-surface on the claw is required, and the film engaging face of the claw must be horizontal at the end of the advancing stroke. Although a claw having a substantially horizontal'film engaging face is preferable, this type of claw is most susceptible to'thev above mentioned disad vantage, that of hopping out of the film perforation during the advancing stroke thereof. This undesirable occurrence is most prevalent at the point where the claw is half way through its advancing stroke, because at this point the film engaging face of the claw is at an angle with relation to the engaged edge of the film perforation so that its natural tendency is to slide out of the film perforation. This angular change of the film engaging face of the claw with respect to the engaged edge of the film perforation is due to the eccentric mounting of said claw. My invention is designed to overcome the above mentioned difficulties and at the same time insure the engagement of the film claw in the film per- 5 foration throughout the film advancing stroke of said claw.

Therefore, one object of this invention is to provide an improved film claw for a ratchet type pull-down mechanism which insures an exact advancing of the film strip regardless of the depth to which the claw penetrates the film perforation at the endof its successive advancing strokes.

Another object is toprovide a film claw whose form positively insures the engagement of claw and the film perforation throughout the advancing stroke of said claw.

Still another object is to provide a claw whose construction permits the elimination of the means commonly used for constantly forcing the claw toward the film strip.

Other objects will appear hereinafter from the following specification, the novel features being pointed out in the claims at the end thereof.

Briefiy, my invention consists of a film claw having a protuberance on its tip which projects vertically below a substantially horizontal film engaging face on the claw, and which extends below the edge of the film perforation engaged by the claw to act as a hook, if the claw tends to leave the film perforation, for positively hold ing said claw in the film perforation until the film advancing stroke is completed. Any of the spring pressing,means as commonly used with pull-downs of this type for pressing the claw towards the film may be used in connection with this new type claw, but no definite limits as to the tension inherent in said spring pressing means is important except that it shall not bethe inherent friction in the bearing of the claw and its reciprocating means which tends to give a constant frictional force which acts on the claw in the direction of the reciprocating means which would be toward the film under normal operating conditions.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which,

Fig. 1 is an enlarged fragmentary side elevation of a camera, partly in section, showing the pull-down mechanism with my novel claw spring pressed against the film; the engaging portion of the claw being exaggerated for the sake of clearness,

Fig. 2 is the same as Fig. 1 with the spring pressing means for the claw omitted, and a modified proturberance being shown on the claw,

Fig. 3 is a fragmentary section of a camera showing the pull down mechanism in elevation with one type of claw found in the prior art,

and a Fig. 4 is a greatly enlarged elevation of the claw in film engaging position at the start 0 its advancing. stroke.

In Fig. 3 a ratchet type pull down mechanism of the prior art is shown for the purpose of comparison with my proposed structure. In this figure a film claw lvis shown eccentrically pivoted to the disc 2 said disc being rotated by the drive shaft 3. As the shaft 3 is rotated, the film claw I is reciprocated vertically through a slot in the partition 4 to engage the perforations of the film strip F at the top of its stroke and advance said film strip an amount equal to its downward stroke. Any type of spring pressed gate Ii may be used to guide the film past the aperture 1 in the partition 4 which is in axial alignment with the objective 8, and to hold the film against the partition so that the claw can engage it properly throughout each advancing stroke thereof.

The disc 2 issituated to one side of the plane -of the film F in the gate 6 so that the undesirable tilting of head of the claw-I at the half way pointpf the advancing stroke due to its eccentric mounting described above, will be eliminated, and the straight edge of the claw I will engage the film substantially at right angles as shown. However, this oifset position of the disc 2 with respect to the plane of the film presents another difiiculty in that witha claw having a straight film engaging face as shown, at the bottom of the film advancing stroke, the film engaging face of the claw will be tipped inward with respect to the plane of the film and any variation in the penetration of the claw and the film perforations at this point in successive strokes of the claw will necessarily cause a variable film advancement which is very undesirable.

The claw is constantly forced toward the film by means of a spring 9 which is suitably mounted on the camera wall III by means of a bracket ll, said spring acting on said claw I through a pin I2 which extends therethrough. This spring pressing means 9 serves two purposes. v First, it acts to constantly force the claw toward the film ,so that it will properly engage the film perforations at the top of its stroke; and secondly, it acts to hold said claw I in engagement with an engaged film perforation throughout the downward'stroke thereof to prevent it from accidentally hopping out thereof before the film advancing stroke is completed. The tension in this spring 9 has to be controlled very closely between two well defined limits. If it is too weak, it fails to hold the claw in the perforation throughout the film advancing stroke, and if it is too strong it tends to force the claw into each engaged film perforation so tightly that the claw cannot leave the perforation cleanly for the upstroke without tending to momentarily reverse 1 the film strip.

This type of claw shown in Fig. 3 and taken from the prior art can be made to work satisfactorily in cameras using slow or normal speeds,

' but in high speed work this type of claw is very unsatisfactory primarily due to the more stringent requirements regarding the tension in the and advanced an amount equal to the downward stroke of the claw. A spring pressed gate I9 is used to guide the film past the aperture in the magazine which is in axial alignment with the objective 2|, and to hold the film against the face as described above. The angle of a face of front of the. magazine so that the claw can engage it properly at each stroke.

In my structure the disc I4 is mounted in the plane of the film F at the gate of the camera so that when the claw I3 is at the bottom of its downward stroke, its point of mounting on the disc M will be in the plane of the film F at the gate. By mounting the disc l4 directly under the film strip as described the ideal condition is attained wherein downward pull on the film en gaging face of the claw l3 at the end of the advancing stroke is directly downward instead of being at an angle as would be the case of an offset mounting as shown by the prior art in Fig. 3.

In order to attain the ideal condition wherein the film strip F is advanced an equal amount at each downward stroke of the claw l3 regardless of the depth of penetration of said claw into the en a ed film perforation at the end of its downward stroke, the film engaging face 28, Fig. 4, of said claw takes the form of an are about a center located by the center ofthe driving shaft l5. This engaging face 28 is substantially horizontal in all positions of the claw l3, but is given a slight arcuate shape to allow for the slight tilting action to which the claw is necessarily subjected on its advancing stroke due to its eccentric mounting on the disc 14. The arcuate face is also provided to account for any. variation in the depth of penetration of said claw with the engaged film perforation, so that regardless to what extent the claw penetrates a film perforation at the end of the advancing stroke it will leave said perforation at identically the same point, relative to the lens system, as it would any successive film perforation. N

In Fig. 2 I have shown the engaging face of the claw modified to one having a straight face. It has been found by calculation that if the engaging face of the claw is straight and has approximately 6 angle with a horizontal through the tip of theclaw it will function almost identically with a claw having an arcuate film engaging this type would necessarilyvary with the dimensions of the several parts going to make up;the

pull-down mechanism so that the scope of my in- I vention should not be limited thereby.

Referring back to Fig. 1, a spring 22 is fastened to the camera frame 23 by a bracket 24, saidspring constantly acting against the pin 25 through the claw l3 to force said claw l3 toward the film so that it will engage the film perforations at the beginning of its downward. stroke,:

and to help hold said claw in the engaged perforation until the downward stroke has been completed. In order to positively insure the engage-- ment of the claw IS with the film perforation throughout the advancing stroke of said claw, I provide the tip of said claw with a suitable protuberance 26, Figs. 1 and 4, which projects below the engaged edge of the film perforation when the claw is in engagement with the film. This protuberance 26 acts as an abutting surface for the film when the claw tends to leave the perforations before the completion of the downward stroke thistendency being most prevalent in the position wherein the claw is half way through its advancing stroke as described in connection with the prior art above.

Figures 1 and 4 show this protuberance 26 in the preferred form, the tip of the protuberance being in the form of a. quarter circle while its sides are parallel to each other and forming an obtuse angle with the film engaging face of the claw. In Fig. 2 a protuberance 26' of modified form is shown, the top of the protuberance being semi-circular while is sides are'substantially perpendicular to the film engaging face of the claw. In Fig. 3, a claw .l of the prior art is shown having a straight film engaging surface, this type of claw relying solely on its spring pressing means 9, of definite tension, for holding it in engagement with the film perforation throughout the film advancing stroke of the claw. V I

In the type of pull-down mechanism shown in Figs. 1 and 2 embodying my proposed type of claw, the tension in the spring pressing means 22 does not have to be controlled between any well defined limits as is necessary with the similar spring pressing means 9 described in connection with the prior art, because my proposed claw I3 is positively held in the engaged film perforation by means of the protuberance 26 instead of by means of the spring 9 as found in the prior art. Since the claw l 3 is positively held in engagement with the film perforations by virtue of the protuberance 26 or 26', Figs. 1 and 2, the use of a strong spring pressing means which is necessary for this purpose in claws of the prior art, as described, is eliminated, and the ensuing disadvantage of this strong spring pressing means, tending to cause a momentary reversal of the film as the claw starts its upstroke, is also eliminated. Therefore, it is readily understandable that a claw of the type proposed is more satisfactory than that shown in connection with the prior art especially for high speed work where the danger of the claw hopping out of the engaged perforations is much more prevalent than at ordinary speeds of operation. Also, in the use of a claw l, as foundfin the prior art, whose engagement with the film perforation during the advancing stroke depends upon a. strong spring pressing means 9, it has been described how closely the tension of this spring 9 must be controlled to allow the claw I to satisfactorily leave the perforation at the start of its upstroke without causing a momentary reversal of the film; and

for this reason a claw of. this type cannot be defilm strip .at all times,- and therebyposition it so that it will enter the film mrforation at the beginning of the film advancing stroke. After the claw l3 has entered the film perforation for. the advancing stroke its engagement with the film perforation is insured.throughout the stroke by the" combined action of the protuberance 26' ,on the 'tip of the claw and the frictional-force emanating from the bearing 21 which constant- 1y forces the claw l3 toward the film strip. This .in the directions of rotation of the disc 14 sufi 'ficient to hold the'claw I 3 in contact with the tension required of the spring 22.

friction in the bearing 21 is relied on for forcing the claw l3 against the film, as shown in Fig. 2, it is desirable to increase the friction in this bearing 21 over that which would be required in the form shown in Fig. 1.

In this proposed type of pull-down mechanism the top of the film claw is constantly held in contact with the film F either through the action of a spring 22, the frictional force in the bearing 21, or both. At the top of its stroke the claw tip 26 or 26' stops its upstroke about .02" above the film perforation to be engaged, and

as the claw starts downward, this tip being the claw tip, which grips the perforation in a hooklike fashion, the film is pulled down an amount equal to the downward stroke of the claw l8. Inasmuch as one of the most essential requirements of a pull-down mechanism of this type is that the claw l3 leaves the successive film perforations'at identically the same point relative to the lens system, and that a variation of penetration of the claw into said film perforation at the end of the stroke would efi'ect this requirement, I have altered the film engaging face of the claw l3 as described above to account for any variation in this penetration so that the claw will have each successive perforation at the same point relative to the lens system.

The top of the claw is cut away at such an angle that as the downward stroke is completed and the upward stroke is started the claw'tip Y leaves the film perforation cleanly so that no Fig. 4 shows the preferred form of the claw I; greatly enlarged for the purpose of clearness. As shown the claw is in engaging position with the film strip F at the start of the advancing stroke and it should be noticed that the face 22 thereof engages the bottom of the perforation substantially parallel to the edge of said perforation. The form of the protuberance 26, shown in Fig. 4 difiers from the protuberance 26' shown in Fig. 2 by having the upper side of the claw ground down to cut the ball tip 26' substantially through its center thereby giving the upper side of the claw a continuous straight line surface from its top to the tip of the protuberance. This construction gives the upper side f the claw a steeper angle and lessens the liabili of the clawattempting to reverse the film strip on its upstroke. Also in this form of the film claw, the inside or filmengaging face of the protuberance 28 is made parallel to the upper face of the, claw instead of substantially vertical asshownl on the protuberance 26' in and, C=.005".

Fig. 2. By way of showing the actual size of these protuberances 26 and 26' with relation to the claw l3, and to emphasize the minuteness of their size, the following dimensions are given. In Fig. 4, the dimension A=.1225", B=.0025", These dimensions are merely given as illustrative of the size of the protuberance with relation to the claw, and. should in no way limit the scope of the invention.

My proposed film claw presents several advantages over those commonly used. First, it allows the use of a claw in which the film engaging face is substantially horizontal so that the advance of the film strip is not altered by any variation in' the depth to which the claw penetrates the film perforations as compared with a film claw having a sharply inclined film engaging surface. Secondly, the engagement of this claw with a film perforation is not dependent upon'any special spring pressing means, the tension in whichhas to be confined within certain well defined limits; in fact the spring pressing means can be entirely omitted without impairing the operation of the apparatus. And last but not least, it provides for the use of a claw having a film engaging face which is substantially parallel to the engaged edge of the film perforations throughout the advancing stroke thereof so that the stress introduced on said engaged edge is distributed acrossthe entire thickness of the film at the perforation instead of being localized on one corner thereof as would be the case if a claw having a sharply inclined film engaging face were used.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and, by. the spirit of the appende 1 claims.

What I claim is:

1. In a motion picture apparatus, the combination with a guideway for supporting a film strip which is provided with perforations, and a film advancing means of the ratchet type including a claw member for intermittently engaging successive perforations of said film strip, and including-an eccentric member for reciprocating said claw member through a pull-down stroke, of a film engaging surface on said claw member, said film engaging surface being substantially straight and adapted to be parallel to the edge of the engaged perforation and substantially normal to the film path at the end of the pull-down stroke, and a'protuberance located at the end of the film engaging surface and extending below the plane of said film engaging surface.

2. In a motion picture apparatus, the combination with a guideway for supporting a film strip which is provided with perforations, and a film advancing means of the ratchet type including a claw member for intermittently engaging successive perforations of said film strip, and including an eccentric member rotatable about an axis within the plane of said film strip in the guideway, and for reciprocatingsaid claw member through a pulldown stroke, of a film engaging surface on said claw member, said film engaging surface being substantially straight and adapted to be parallel to the edge of the engaged perforation and substantially normal to the film path at the end of the pull-down stroke, and a protuberance located at theend of the film engaging surface and extending below the plane of said film engaging surface.

3. In a motion picture apparatus operable at high speeds, the combination with a guideway for supporting a film strip provided with-perforations, a ratchet Haw member for intermittently engaging successive perforations of said film strip, an eccentricnirnber for reciprocating said claw member through a cycle comprising a pull down stroke and a return, stroke and a tendency perforation and substantially normal to the film I path at the end of the pull-down stroke, and a protuberance located at the end of the film 25 engaging surface and extending below the plane of said film engaging surface.

4. In a motion picture apparatus operable at high speeds, the combination with a guideway for supporting a film strip provided with perfora- 30 tions, a ratchet claw member for intermittently engaging successive perforations of said film strip, an eccentric member for reciprocating said claw member through a cycle comprising a pulldown stroke and a return stroke and a spring 35 member exerting upon said ratchet claw member a. resilient force sufficient to move the same into engagement with one of said perforations at the commencement of said pull-downstroke but insufiicient to cause. retrograde duction of the film strip during the return stroke of said ratchet claw member particularly upon operation of said high speeds, of a film engaging surface on said claw member, said film engaging surface being substantially straight and adapted to be substan tially parallel to the edge of the engaged perforation and substantially normal to the film path at the end' of the pull-down stroke, and a protuberance located at the end of the film engaging surface and extending below the plane of said film engaging surface.

5. In a motion picture apparatus, the combina-' tion with a guideway for supporting a film strip provided with perforations, a ratchet claw mem-.

ber for intermittently engaging successive per-' forations of said film strip, an eccentric member for reciprocating said clawmember through a cycle comprising a pull-down stroke and a return stroke, and a connection between said clawand eccentric member and having sufficient friction to cause said claw member to move into engagement at the commencement of said pull-down stroke, of a film engaging surface on said claw member, said film engaging surface being substantially straight and adapted to be substantially parallel to the edge of the engaged perforation and substantially normal to the film path at the end of the pull-down stroke, and a protuberance located at the end of the film engaging surface and extending below the plane of said film. engaging surface.

O'I'I'O WITTEL. 

